Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave-diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression stops. A distinction is made by recreational diver training agencies between cave-diving and cavern-diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
In the United Kingdom, cave-diving developed from the locally more common activity of caving. Its origins in the United States are more closely associated to recreational scuba diving. Compared to caving and scuba diving, there are relatively few practitioners of cave-diving. This is due in part to the specialized equipment and skill sets required, and in part because of the high potential risks due to the specific environment.
Despite these risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can contain fauna not found elsewhere.
The procedures of cave-diving have much in common with procedures used for other types of penetration diving. They differ from open-water diving procedures mainly in the emphasis on navigation, gas management, operating in confined spaces, and that the diver is physically constrained from direct ascent to the surface during much of the dive.
As most cave-diving is done in an environment where there is no free surface with breathable air allowing an above-water exit, it is critically important to be able to find the way out before the breathing gas runs out. This is ensured by the use of a continuous guideline between the dive team and a point outside of the flooded part of the cave, and diligent planning and monitoring of gas supplies. Two basic types of guideline are used: permanent lines, and temporary lines. Permanent lines may include a main line starting near the entrance/exit, and side lines or branch lines, and are marked to indicate the direction along the line to the nearest exit. Temporary lines include exploration lines and jump lines.
Decompression procedures may take into account that the cave diver usually follows a very rigidly constrained and precisely defined route, both into and out of the cave, and can reasonably expect to find any equipment such as drop cylinders temporarily stored along the guideline while making the exit. In some caves, changes of depth of the cave along the dive route will constrain decompression depths, and gas mixtures and decompression schedules can be tailored to take this into account.
Main article: Scuba skills
Most open-water diving skills apply to cave-diving, and there are additional skills specific to the environment, and to the chosen equipment configuration.
See also: Distance line § Procedures
The essential cave-diving procedure is navigation using a guide line. This includes laying and marking line, following line and interpreting line markers, avoiding entanglement, recovering from entanglement, maintaining and repairing line, finding lost line, jumping gaps, and recovering line, any of which may need to be done in zero visibility, total darkness, tight confined spaces or a combination of these conditions.
Losing the guide line in a cave is a potentially life-threatening emergency. While following recommended best practice makes it highly unlikely that a diver will lose the line, it can and does happen, and there are procedures which will usually work to find it again. Any reliable information on where the diver is likely to be relative to the last known position of the line may be critical, and the procedure of choice will depend on what is reliably known. In all situations, the diver will attempt to stabilise the situation and avoid getting further lost, and make a thorough visual check in all directions from where they are at the time, taking into account the possibility of the line being in a line trap. If the diver has not also separated from their buddy, the buddy may know where the line is, and can be asked, and if the diver is separated from their buddy, the buddy may be at the line, and the buddy's light may be visible.
Stabilising the position is generally done by finding the nearest feasible tie-off point and securely tying off a search line. The direction of the guide line when last seen should be known, and therefore the direction the diver was swimming in before losing the line. If the diver was neutrally buoyant while following the line, the approximate depth can be reconstructed by finding the depth of neutral buoyancy again, without adjusting inflation of BCD or dry suit. Unless the line was lost by the diver not noticing a change of direction, it is likely to be at much the same depth, in much the same direction, and at a similar lateral and vertical distance as when last seen, making it logical to try that direction first. While swimming towards the estimated position of the line and slowly paying out search line, the diver will search visually, and in low visibility or darkness, also by feel, making arm sweeps across the expected direction of the line, while defending the head from impact with the other arm. The distance swum towards the estimated position of the lost line can be measured by the spacing and number of knots paid out on the search line. If the search fails, the diver will return to the tie off and try again in the next best guess for the direction the line may be. The diver may also choose to try a different search method. The best search method for any given situation will depend on the water conditions, the layout of the section of cave, the way the line was laid, the situational knowledge and skills of the diver, and the equipment available – a method that would be ideal for one situation might not work at all for another.
If the line is found, but not the other divers, the diver can tie off their search reel to the guide line as an indicator to other members of the team that they were lost but have found the guide line, and indicate the direction that they intend to proceed along the guideline with a personal directional marker so that others who see it while searching for the lost diver will know whether the diver chose the right direction to exit the cave.
This is generally the converse situation to the lost guide line, in that the diver loses contact with their buddy or team but remains in contact with the guide line, so is not themselves lost. Their first priority is to not get lost or disorientated, and in furtherance of this aim would attach a directional line marker to the guide line indicating the direction to the exit before starting a search. The search line can be tied to the directional maker to prevent it from sliding along the line during the search. The direction for the search would depend on the layout of that part of the cave, and where the missing diver should have been in the group. The search party must consider their own safety first, regarding how much gas they can afford to use in a search, which will depend on the stage of the dive when the diver is noticed to be missing. When searching in darkness, the searches should periodically turn off their lights as this will allow them to see the lost diver's light more easily.
Main articles: Scuba gas planning and Scuba gas management
Gas planning is the aspect of dive planning which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive profile. It usually assumes that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure based on a fraction of the initial gas supply is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.
Gas planning includes the following aspects:: Sect.3
The primary breathing apparatus may be open circuit scuba or rebreather, and bailout may also be open circuit or rebreather. Emergency gas may be shared among the team members, or each diver may carry their own, but in all cases each diver must be able to bail out onto a gas supply of their own for long enough to get to the next planned source of emergency gas. If for any reason this situation no longer applies, there is a single point of critical failure, and the risk becomes unacceptable, so the dive should be turned.
Gas management also includes the blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, and the monitoring and switching of breathing gases during a dive, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations and oxygen toxicity risk.
The rule of thirds for gas management is a rule of thumb used by divers to plan dives so they have enough breathing gas remaining in their diving cylinder at the end of the dive to be able to complete the dive safely. This rule mostly applies to diving in overhead environments, such as caves and wrecks, where a direct ascent to the surface is impossible and the divers must return the way they came.
For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve. However, when diving with a buddy with a higher breathing rate or a different volume of gas, it may be necessary to set one third of the buddy's gas supply as the remaining 'third'. This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.
A different option for penetration dives is the Half + 15 bar (half + 200 psi) method, in which the contingency gas for the stage is carried in the primary cylinders. Some divers consider this method to be the most conservative when multi-staging. If all goes to plan when using this method, the divers surface with stages nearly empty, but with all the contingency gas still in their primary cylinders. With a single stage drop, this means the primary cylinders will still be about half-full.
Cave-diving training includes equipment selection and configuration, guideline protocols and techniques, gas management protocols, communication techniques, propulsion techniques, emergency management protocols, and psychological education.[clarification needed] Cave diver training also stresses the importance of risk management and cave conservation ethics. Most training systems offer progressive stages of education and certification.
A significant aspect of cave diving by competent and enthusiastic cave divers is exploration, survey and mapping. Data collected is often shared and may be stored on databases to help optimise the effectiveness of such surveys, and make the information generally available.
Underwater cave mapping is complicated by both a lack of access to the surface for GPS positions, darkness, with short line-of-sight, and limited visibility, which complicate optical measurement. Altitude/depth is relatively simple as accurate depth measurement is available to divers in the form of decompression computers, which log a depth/time record of reasonable accuracy and are available for instantaneous readout at any point, and depth can be referenced to the altitude at the surface. Vertical dimensions can be directly measured or calculated as differences in depth.
Surface coordinates can be collected via GPS and remote sensing, with varying degrees of precision and accuracy depending on the type of entrance. In some caves the water surface is in view of GPS satellites, in others it is a considerable distance along a complex route from the nearest open air. Three dimensional models of varying accuracy and detail can be created by processing measurements collected by whatever methods were available. These can be used in virtual reality models. The usual methods for survey and mapping of underwater caves are dead reckoning and direct measurements of distance, compass direction and depth, by diving teams of two or three scuba divers, who record azimuth of the cave line, measurements of height, width, depth, and slope at intervals along the line, generally using a permanent guide line as a reference baseline, and take photographic records of features and objects of interest. Data are collected on wet-notes and by digital photography. Hand-held sonar may be used for distance measurement where available. Where the depth or other constraints prevent divers from exploring in person, tethered and untethered remotely operated underwater vehicles (ROUVs) have been used effectively, using sonar technology to scan and map the surroundings, and video to record the appearance.
Features, artifacts, remains, and other objects of interest are recorded in situ as effectively as possible, generally by photography.
Cave-diving is one of the most challenging and potentially dangerous kinds of diving and presents many hazards. Cave-diving is a form of penetration diving, meaning that in an emergency a diver cannot swim vertically to the surface due to the cave's ceilings, and so must swim the entire way back out. The underwater navigation through the cave system may be difficult and exit routes may be at a considerable distance, requiring the diver to have sufficient breathing gas to make the journey. The dive may also be deep, resulting in potential deep diving risks.
Visibility can vary from nearly unlimited to low, or non-existent, and can go from very good to very bad in a single dive. While a less-intensive kind of diving called cavern diving does not take divers beyond the reach of natural light (and typically no deeper than 30 metres (100 feet)), and penetration not further than 60 m (200 ft), true cave-diving can involve penetrations of many thousands of feet, well beyond the reach of sunlight. The level of darkness experienced creates an environment impossible to see in without an artificial source of light even if the water is clear. Caves often contain sand, mud, clay, silt, or other sediment that can further reduce underwater visibility in seconds when stirred up. Consequently, visibility is often worse during exit, and divers rely on the guideline for finding the way out.
The water in caves can have strong flow. Most caves flooded to the surface at the cave mouth are either springs or siphons. Springs have out-flowing currents, where water is coming up out of the Earth and flowing out across the land's surface. Siphons have in-flowing currents where, for example, an above-ground river is going underground. Some caves are complex and have some tunnels with out-flowing currents, and other tunnels with in-flowing currents. Inflowing currents can cause serious problems for the diver, as they make the exit more difficult, and the diver is carried to spaces that are unfamiliar and may be dangerous, while outflowing currents generally make the exit quicker and the diver is carried through places they have been before and can be prepared for difficult areas.
Cave-diving has been perceived as one of the more deadly sports in the world. This perception may be exaggerated because the majority of divers who have died in caves have either not undergone specialized training or have had inadequate equipment for the environment. Some cave divers have suggested that cave-diving is statistically much safer than recreational diving due to the much larger barriers imposed by experience, training and equipment cost, but there is no definitive statistical evidence for this claim.
There is no reliable worldwide database listing all cave-diving fatalities. Such fractional statistics as are available, however, suggest that few divers have died while following accepted protocols and while using equipment configurations recognized as acceptable by the cave-diving community. In the very rare cases of exceptions to this rule there have typically been unusual circumstances.
Main article: Diving safety
Most cave divers recognize five general rules or contributing factors for safe cave-diving, which were popularized, adapted and became generally accepted from Sheck Exley's 1979 publication Basic Cave Diving: A Blueprint for Survival. In this book, Exley included accounts of actual cave-diving accidents, and followed each one with a breakdown of what factors contributed to the accident. Despite the unique circumstances of each individual accident, Exley found that at least one of a small number of major factors contributed to each one. This technique for breaking down accident reports and finding common causes among them is now called accident analysis, and is taught in introductory cave-diving courses. Exley outlined a number of these resulting cave-diving rules, but today these five are the most recognized:
Most cave-diving fatalities are due to running out of gas before reaching the exit. This is often the direct consequence of getting lost, whether the guide line is found again or not, and whether the visibility deteriorates, lights fail, or someone panics. On rare occasions equipment failure is unrecoverable, or a diver becomes inextricably trapped, seriously injured, incapacitated by using an unsuitable gas for the depth, or swept away by strong flow. Getting lost means separation from the continuous guide line to the exit, and not knowing the direction to the exit.
Some cave divers are taught to remember the five key components with the mnemonic: "The Good Divers Always Live" (training, guide, depth, air, light).
In recent years new contributing factors were considered after reviewing accidents involving solo diving, diving with incapable dive partners, video or photography in caves, complex cave dives and cave-diving in large groups. With the establishment of technical diving, the use of mixed gases—such as trimix for bottom gas, and nitrox and oxygen for decompression—reduces the margin for error. Accident analysis suggests that breathing the wrong gas for the depth or not analyzing the breathing gas properly has also led to cave-diving accidents.
Cave-diving requires a variety of specialized procedures, and divers who do not correctly apply these procedures may significantly increase the risk to the members of their team. The cave-diving community works hard to educate the public on the risks they assume when they enter water-filled caves. Warning signs with the likenesses of the Grim Reaper have been placed just inside the openings of many popular caves in the US and Mexico, and others have been placed in nearby parking lots and local dive shops.
Many cave-diving sites around the world include open-water basins, which are popular open-water diving sites. The management of these sites try to minimize the risk of untrained divers being tempted to venture inside the cave systems. With the support of the cave-diving community, many of these sites enforce a "no-lights rule" for divers who lack cave training—they may not carry any lights into the water with them. It is easy to venture into an underwater cave with a light and not realize how far away from the entrance (and daylight) one has swum; this rule is based on the theory that, without a light, divers will not venture beyond daylight.
In the early phases of cave-diving the analysis shows that 90% of accidents were not trained cave divers; from the 2000s on the trend has reversed to 80% of accidents involving trained cave divers. Modern cave divers' capability and available technology allows divers to venture well beyond traditional training limits[clarification needed] and into actual exploration. The result is an increase of cave-diving accidents, in 2011 the yearly average of 2.5 fatalities a year tripled. In 2012 fatalities reached the highest annual rate to that date at over 20.
As response to the increase in fatalities during the years 2010 onwards, the International Diving Research and Exploration Organization (IDREO) was created in order to "bring awareness of the current safety situation of Cave Diving" by listing current worldwide accidents by year and promoting a community discussion and analysis of accidents through a "Cave Diver Safety Meeting" held annually.
See also: Diving equipment
Equipment used by cave divers ranges from fairly standard recreational scuba configurations, to more complex arrangements which allow more freedom of movement in confined spaces, extended range in terms of depth and time, allowing greater distances to be covered in acceptable safety, and equipment which helps with navigation, in what are usually dark, and often silty and convoluted spaces.
Scuba configurations which are more often found in cave-diving than in open water diving include independent or manifolded twin cylinder rigs, side-mount harnesses, sling cylinders, rebreathers and backplate and wing harnesses. Bill Stone designed and used epoxy composite tanks for exploration of the San Agustín and Sistema Huautla caves in Mexico to decrease the weight for dry sections and vertical passages.
Stage cylinders are cylinders which are used to provide gas for a portion of the penetration. They may be deposited on the bottom at the guideline on preparation dives, to be picked up for use during the main dive, or may be carried by the divers and dropped off at the line during the penetration to be retrieved on the way out.
One of the high risk hazards of cave-diving is getting lost in the cave. The use of guide lines is the standard mitigation for this risk. Guide lines may be permanent or laid and recovered during the dive, using cave reels to deploy and recover the line. Permanent branch lines may be laid with a gap between the start of the branch line and the nearest point on the main line. Line used for this purpose is known as cave line. Gap spools with a relatively short line are commonly used to make the jump.
Line arrows are used to point towards the nearest exit, and cookies are used to indicate use of a line by a team of divers.
Silt screws are short lengths of rigid tube (usually plastic) with one sharpened end and a notch or slot at the other end to secure the line, which are pushed into the silt or detritus of the cave floor as a place to tie off a guideline when no suitable natural tie-off points are available.
A simple plastic helmet, such as those used in water sports like whitewater kayaking, is good protection in case of accidental contact with the cave ceiling or stalactites.
Diver propulsion vehicles, or Scooters, are sometimes used to extend the range by reducing the work load on the diver and allowing faster travel in open sections of cave. Reliability of the diver propulsion vehicle is very important, as a failure could compromise the ability of the diver to exit the cave before running out of gas. Where this is a significant risk, divers may tow a spare scooter.
Dive lights are critical safety equipment, as it is dark inside caves. Each diver generally carries a primary light, and at least one backup light. A minimum of three lights is recommended. The primary light should last the planned duration of the dive, as should each of the backup lights.
Cavern diving is an arbitrarily defined, limited scope activity of diving in the naturally illuminated part of underwater caves, where the risk of getting lost is small, as the exit can be seen, and the equipment needed is reduced due to the limited distance to surface air. It is defined as a recreational diving activity as opposed to a technical diving activity on the grounds of low risk and basic equipment requirements.
Jacques-Yves Cousteau, co-inventor of the first commercially successful open circuit scuba equipment, was the world's first open circuit scuba cave diver. However, many cave divers penetrated caves prior to the advent of scuba with surface supplied breathing apparatus through the use of umbilical hoses and compressors. SCUBA diving in all its forms, including cave-diving, has advanced in earnest since Cousteau introduced the Aqua-Lung in 1943.
Two regions have had particular influence on cave-diving techniques and equipment due to their very different cave-diving environments. These are the United Kingdom, and the United States, mainly Florida.
The Cave Diving Group (CDG) was established informally in the United Kingdom in 1935 to organise training and equipment for the exploration of flooded caves in the Mendip Hills of Somerset. The first dive was made by Jack Sheppard on 4 October 1936, using a home-made drysuit surface fed from a modified bicycle pump, which allowed Sheppard to pass Sump 1 of Swildon's Hole. Swildon's is an upstream feeder to the Wookey Hole resurgence system. The difficulty of access to the sump in Swildon's prompted operations to move to the resurgence, and the larger cave there allowed use of standard diving dress which was secured from the Siebe Gorman company. In UK cave-diving, the term "Sherpa" was used without irony for the people who carry the diver's gear although this has gone out of fashion; support is now more normally used, and before the development of SCUBA equipment such undertakings could be monumental operations.
Diving in the spacious third chamber of Wookey Hole led to a rapid series of advances, each of which was dignified by being given a successive number, until an air surface was reached at what is now known as "Chamber 9." Some of these dives were broadcast live on BBC radio, which must have been a quite surreal experience for both diver and audience.
The number of sites where standard diving dress could be used is clearly limited and there was little further progress before the outbreak of World War II reduced the caving community considerably. However, the rapid development of underwater warfare through the war made a lot of surplus equipment available. The CDG re-formed in 1946 and progress was rapid. Typical equipment at this time was a frogman rubber diving suit for insulation (water temperature in the UK is typically 4 °C), an oxygen diving cylinder, soda lime absorbent canister and counter-lung comprising a rebreather air system and an "AFLOLAUN", meaning "Apparatus For Laying Out Line And Underwater Navigation." The AFLOLAUN consisted of lights, line-reel, compass, notebook (for the survey), batteries, and more.
Progress was typically by "bottom walking", as this was considered less dangerous than swimming (note the absence of buoyancy controls). The use of oxygen put a depth limit on the dive, which was considerably compensated by the extended dive duration. This was the normal diving equipment and methods until approximately 1960 when new techniques using wetsuits (which provide both insulation and buoyancy ), twin open-circuit SCUBA air systems the development of side mounting cylinders, helmet-mounted lights and free-swimming with fins. The increasing capacity and pressure rating of air bottles also extended dive durations.
In the 1970s, cave-diving greatly increased in popularity among divers in the United States. However, there were very few experienced cave divers and almost no formal classes to handle the surge in interest. The result was a large number of divers trying to cave dive without any formal training. This resulted in more than 100 fatalities over the course of the decade. The state of Florida came close to banning SCUBA diving around the cave entrances. The cave-diving organizations responded to the problem by creating training programs and certifying instructors, in addition to other measures to try to prevent these fatalities. This included posting signs, adding no-lights rules, and other enforcements.
In the United States, Sheck Exley was a pioneering cave diver who first explored many underwater cave systems in Florida, and many throughout the US and the world. On 6 February 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society.
Since the 1980s, cave-diving education has greatly reduced diver fatalities, and it is now rare for an agency trained diver to perish in an underwater cave. Also in the 1980s, refinements were made to the equipment used for cave-diving, most importantly better lights with smaller batteries. In the 1990s, cave-diving equipment configurations became more standardized, due mostly to the adaptation and popularization of the "Hogarthian Rig", developed by several North Florida cave divers, named in honor of William "Hogarth" Main, which promotes equipment choices that "keep it simple and streamlined".
Today,[when?] the cave community is most focused on training, exploration, public awareness, and cave conservation.
Documentary films made by Wesley C. Skiles and Jill Heinerth have contributed to the increasing popularity of cave-diving in the early 21st century.
Four divers using scuba dived from the Right Imperial Cave in the Jenolan system in the Blue Mountains to an upstream chamber on 30 October 1954.
Main article: Cave diving regions of the world
Cave-diving venues can be found on all continents except Antarctica, where the average temperature is too low for water to remain liquid in caves.
There are few flooded caves in Africa which are known and accessible. There are several in South Africa, a few in Namibia and Zimbabwe, and some large caves recently discovered in Madagascar.
There are a large number of flooded caves in the limestone regions and other regions of Asia, particularly in the karst regions of China and Southeast Asia. Some are accessible for recreational cave-diving, but most have probably not yet been found or explored.
Australia has many spectacular water filled caves and sinkholes, many of them in the Mount Gambier region of South Australia.
Europe has a large number of flooded caves, particularly in the karst regions.
North America has many cave-diving venues, particularly in Florida, USA, and the Yucatán Peninsula of Mexico.
South America has some cave-diving venues in Brazil.
See also: Glossary of caving and speleology
Caves and caverns as geographical entities are defined differently from cave-diving and cavern-diving, so it is possible to be cavern diving in what is technically a cave, and cave-diving in what is technically a cavern.
A cave dive can be categorised by the topology of the route, which can be linear, include a circuit, or be a traverse.
These terms describe flooded cave areas with reference to flow direction.
Cave where water flows out of the entrance used for diving. The flow will generally help divers on the way out.
A cave where water flows into the entrance used for diving, which can hinder divers from getting out.
A locally low-lying water filled passage of a cave. A cave may have several sumps separated by unflooded or partially flooded areas.
Main article: Cave
Cave caused by wind erosion.
Flooded mines and other underground spaces excavated by people and their machinery, by technical definition are not caves, but the activity of diving in such spaces is considered cave-diving, as the procedures and equipment are the same.
Caves caused by volcanic action, where a lava flow cools and solidifies on the outside, and the fluid interior lava flows out at the lower end when the supply stops. They may be branched, but are usually continuously sloped. Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, inflationary, and blister caves.
Cave along the shore of a coastal area. Usually created by wave action, and may be affected by tidal currents and wave surge.
Cave formed by groundwater dissolving the rock over long periods. They are more common in rocks which are more soluble in mildly acidic water, such as limestones and dolomites, and may be common in karst regions.
Cave formed by rock falls.
Notable cave divers:
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